ATCA Selfcal Issue

Accidental application of on-line SelfCal

In 2006 the command "selfcal on/off" was added to CAOBS to allow
selfcalibration of the array in tied array mode (for NASA tracking). We
recently noticed that this mode could be switched on accidentally by
typing e.g. "sel aa" (a VIS command) in the CAOBS window. Going back
through the logs we've found that 5 observations have been affected by
this. The CAOBS problem has now been fixed and a miriad task "atscfix" has
been written to correct the data.

The effect of the on-line selfcal is visible on calibrators, the phases
gets calibrated to near zero every 2nd integration cycle. For weak sources
the phases have 'random' offsets applied every 2 cycles. Note that only
the first frequency band of dual frequency observations is affected.

Reload the data using atlod, selecting the first frequency band with
ifsel=1

Copy the file with selfcal corrections from the list below to your
working directory (name it selfcal.txt or similar)

Run the atscfix program using the following command:
atscfix vis=mydataf1.uv out=mydataf1-fix.uv scphase=selfcal.txt offset=10

Use the cycle period (integration time of visibilities) of your observation for the offset parameter.

This should restore the phases to a continuous sequence. Depending on
where in the data you did your cacal, a constant phase offset may be
introduced, but this should calibrate out with normal offline calibration.